Segmental relaxation mode

Radiation processes No effect (unless chain scission occurs, which significantly affects segmental relaxation modes) Irregular dependence (usually lowering of the signal due to neutralization of carriers from radiation-induced charges)... 

The scaling results above all pertain to local segmental relaxation, with the exception of the viscosity data in Figure 24.5. Higher temperature and lower times involve the chain dynamics, described, for example, by Rouse and reptation models [22,89]. These chain modes, as discussed above, have different T- and P-dependences than local segmental relaxation. 

The earliest and simplest approach in this direction starts from Langevin equations with solutions comprising a spectrum of relaxation modes [1-4], Special features are the incorporation of entropic forces (Rouse model, [6]) which relax fluctuations of reduced entropy, and of hydrodynamic interactions (Zimm model, [7]) which couple segmental motions via long-range backflow fields in polymer solutions, and the inclusion of topological constraints or entanglements (reptation or tube model, [8-10]) which are mutually imposed within a dense ensemble of chains. 

Dielectric spectroscopy was also used by the same group in order to study the local and global dynamics of the PI arm of the same miktoarm star samples [89]. Measurements were confined to the ordered state, where the dynamics of the PI chain tethered on PS cylinders were observed in different environments since in the SIB case the faster moving PB chains are tethered in the same point as the PI arm. The distribution of segmental relaxation times were broader for SI2 than SIB. The effect was less pronounced at higher temperatures. The PI normal mode time was found to be slower in SIB, when compared to SI2 although both arms had the same molecular weight. Additionally, the normal mode relaxation time distributions of the PI chains tethered to PS cylinders in the miktoarm samples were narrower than in P(S-h-I) systems of lamellar structure. 

In this section, we compare the normal mode relaxation with the segmental relaxation, and discuss another remarkable property that emerges from the comparison. The property is best described by the figure published by Arrese-Igor et al. (2011), which is reproduced here as Figure 5.30. In this figure, /max,NM 0.5 Hz is the same for all blends ranging from pure PI to 20%... 

The MCT theory assumes a cell-like structure in which the main relaxation process is segmental the particles vibrate at high frequency either inside their cell-like domains or jump between them. As T decreases below Tc, the structural relaxation mode takes over. The latter mode persists to temperatures well below Tg, where the fast elementary relaxations characteristic of polymers are present. At T< Tg, immobile clusters and mobile defects dominate the material behavior [Kanaya and Kaji, 2001 Binder et al., 2003]. 

For further examination of the segmental length scale for PVE in the PI/PVE blends, Hirose et al. (2004) analyzed the broadness of the dielectric mode distribution observed as the co dependence of the e" data. As an example. Figure 3.12 shows co dependence of the e" data at 10°C measured for a PI/PVE blend with Mp, = 1.2 x 10, Mpyp = 6 x 10, and Wp, = 17 wt% (circles). Because of this small Wpi value, the relaxation seen in Figure 3.12 is almost exclusively attributed to the segmental motion of PVE in the blend. The dielectric segmental relaxation of bulk PVE is satisfactorily described by the Havriliak-Negami (HN) empirical equation (Hirose et al., 2004) ... 

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